Adhesive formulations containing urea additives, methods of forming plywood therewith, and plywood products made thereby

Abstract

Compositions suitable for use as wood adhesives are described, which compositions comprise: (a) a polymeric component selected from the group consisting of lignins, proteins, and mixtures thereof, (b) an adhesion promoter comprising at least one component selected from the group consisting of (i) adducts of an epoxide and a resin selected from the group consisting of polyamine resins, polyamidoamine resins, polyamide resins, and combinations thereof, and (ii) combinations of a curing agent and a compound having at least one amine, amide, imine, imide, or nitrogen-containing heterocyclic functional group capable of reacting with at least one functional group of the polymeric component; and (c) an additive selected from the group consisting of urea, N-substituted ureas, N,N-disubstituted ureas, N,N′-disubstituted ureas, N,N,N′-trisubstituted ureas, N,N,N′,N′-tetrasubstituted ureas, urea derivatives, and mixtures thereof.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 60 / 896,614, filed on Mar. 23, 2007, the entire contents of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]Composite and laminate wood-based products are widely used throughout the world in construction projects, both commercial and residential. Composite wood products are generally formed by providing a mixture of small dimension pieces of cellulosic material, which can be fragmented from solid wood into strands, fibers, and / or chips (often referred to collectively as “wood particles”), and an adhesive composition, and subsequently the mixture is subjected to heat and pressure to produce a composite wood sheet such as particle board, wafer board or oriented strand board. Laminate wood products, such as plywood, are usually prepared by adhering a higher quality or hardwood surface veneer layer to a core subs...

AI Technical Summary

Benefits of technology

[0008]The present invention relates, in general, to the surprising discovery that the addition of a urea additive to various compositions used as wood adhesives which comprise substantially formaldehyde-free adhesion promoters and protein and / or lignin components, can reduce or visibly eliminate staining along hardwood veneer splice lines containing urea-formaldehyde resins.

[0014]The use of compositions according to the present invention can provide significant economic benefits to plywood producers by allowing them to employ substrates and adhesives that are more environmentally acceptable and still prepare hardwood panels with UF-spliced surface veneers while avoiding undesirable staining.

Problems solved by technology

However, there are concerns with the use of PF and UF resins.

However, the use of such formaldehyde-free adhesive formulations is not always ideal.

One problem confronting the composite and laminate wood industry in use of such environmentally acceptable adhesives is the formation of color in plywood made with such PAE-soy adhesive systems.

Moreover, the staining can transfer to adjacent boards when the panels are stacked without complete cooling after the bonding of the veneer layer.

The discoloring produced along the splice lines is aesthetically unsatisfactory to the consumer, thus significantly reducing the value of the panels, and the discoloring also reduces the economy of production for the industry.

While attempts have been made to reduce the problem of splice line staining by employing alternative adhesives for the production of hardwood veneer layers, the quality of splicing using non-urea formaldehyde resins with hardwood materials has been less than satisfactory.

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